With an incandescent bulb you bought by watts. With LED you look at lumens. But what exactly is a lumen, how many lumens do you need, and what is the difference with watts and lux? In this guide I explain it with a conversion table and a worked example.
In short
- Lumens (lm): the total amount of light a lamp gives off. This determines how bright the lamp is.
- Watts (W): how much power the lamp uses. With LED this says little about brightness.
- Lux (lx): how much light falls on a surface, in lumens per square metre.
- The sum: the lumens you need are roughly lux times the number of square metres.
Jump straight to:
Lumens, watts and lux: what is the difference?
Lumens
Lumens measure a lamp's total luminous flux: all the light it gives off in every direction. More lumens means a brighter lamp. With a spot, the beam angle matters too, because a narrow beam concentrates the same lumens on a smaller area.
Watts
Watts measure power consumption, not brightness. With incandescent bulbs a given wattage came with roughly the same brightness, which is why we bought by watts. An LED achieves the same light with a fraction of the power, so wattage is no longer a good measure.
Lux
Lux is the amount of light that falls on a surface: 1 lux is 1 lumen per square metre. The same lamp gives more lux if you hang it closer to your desk. That is why lux tells you how well you can see in a given spot.
Lumens per watt
This is the lamp's efficiency. An incandescent bulb manages around 12 to 15 lumens per watt, a good LED easily 100 lumens per watt or more. The higher, the more economical. On the energy label this is converted into a letter.
From watts to lumens: conversion table
These values are a guideline for replacing your old lamp. Always check the lumen value on the packaging.
| Old incandescent bulb | Approx. lumens | LED replacement |
|---|---|---|
| 25 watts | 250 lm | 2 to 3 watts |
| 40 watts | 400 to 470 lm | 4 to 5 watts |
| 60 watts | 700 to 810 lm | 6 to 9 watts |
| 75 watts | 1000 to 1100 lm | 9 to 12 watts |
| 100 watts | 1500 to 1600 lm | 13 to 16 watts |
How many lumens do I need?
Calculate it like this: desired lux times the area in square metres. A 20 m² living room where you want 150 lux then needs about 3000 lumens. Add a little to be safe, because part of the light is lost in the fitting and on dark walls. These target values are a good start:
Per room
Bedroom: 50 to 100 lux. Living room: 100 to 200 lux. Hallway and landing: about 100 lux. Bathroom: 200 to 300 lux. Kitchen: 300 to 500 lux on the worktop. Desk and office: around 500 lux. Workshop: 300 to 750 lux. Take a look at the room collections for the living room, kitchen and office.
Light colour and quality
Besides brightness, the colour of the light matters. You can read more about that in LED colour temperature. You will find more terms in the LED alphabet.
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Frequently asked questions
What is a lumen?
How many lumens is a 60-watt bulb?
How many lumens do I need in the living room?
What is the difference between lumens and lux?
Are more lumens always better?
Kind regards,
Bas / LEDPLANET.NL